Liquid crystal projectors are widely used as a video display apparatus with a large screen by which light modulated on a liquid crystal panel in response to a video signal is projected from a projection lens after light from a light source has been irradiated on a liquid crystal panel.
In a three-chip type liquid crystal projector using three liquid crystal panels corresponding to three colors of R (red), G (green) and B (blue), light from a light source is separated into lights of respective colors of R, G and B by a suitable means such as a dichroic mirror and these lights are irradiated on the liquid crystal panels corresponding to the respective colors R, G and B.
Also, in a single-chip type liquid crystal projector using a single liquid crystal panel, light irradiated on the liquid crystal panel from a light source is separated into lights of respective colors of R, G, and B by a color filter attached to the liquid crystal panel.
So far, a super-high-pressure mercury lamp has been the main stream of the light source of this liquid crystal projector. FIG. 1 is a diagram showing a distribution of a light emission spectrum of a super-high-pressure mercury lamp. The light emission spectrum of the super-high-pressure mercury lamp has energy peaks at a wavelength region ranging from 400 to 480 nm and at a wavelength region ranging from 490 to 550 nm. Light in the wavelength region ranging from 400 to 480 nm is used as blue light and light in the wavelength region ranging from 490 to 550 nm is used as green light. Also, light in the wavelength region ranging from 620 to 700 nm is used as red light.
However, the liquid crystal projector according to the related-art has encountered with the following problems (a) and (b).
(a) As shown in FIG. 1, in the super-high-pressure mercury lamp, intensity of a red light component is relatively low as compared with that of a green light component or a blue light component. Accordingly, while balance of a picture projected from the liquid crystal projector is deviated in the direction of green or blue so that the green light component or the blue light component should be decreased considerably in order to maintain white balance. As a consequence, the liquid crystal projector according to the related art becomes unable to display a picture with sufficiently high luminance.
(b) The life span of the super-high-pressure mercury lamp is relatively short and it lies in a range of from about 1000 to 2000 hours. Therefore, maintenance for changing a light source should be executed comparatively frequently.
While liquid crystal projectors using a metal halide lamp as a light source are available on the market as a liquid crystal projector according to the related art, it is unavoidable that such liquid crystal projector also encounters with the above-described problems (a) and (b).
As one method for solving the problem in which the picture has low luminance because the color components are not uniform in intensity and the problem in which the life span of the light source is short, it is considered to use an LED (light-emitting diode) as a light source of a liquid crystal projector instead of using the discharge lamp such as the super-high-pressure mercury lamp and the metal halide lamp.
That is, since a blue LED becomes commercially available on the market in recent years, the LED can obtain lights of respective colors of R, G, and B with arbitrary intensity each and the life span of such light-emitting diode is considerably long so that it can be energized and de-energized continuously for several 10000s of hours.
However, the LED has remarkably small light emission intensity per unit area as compared with that of the discharge lamp. Therefore, a large number of LEDs should be used to realize a light source with high luminance.
One of the characteristics that should be required by a light source for use with a projection type display apparatus such as a liquid crystal projector may be “light source should have a small emission area as much as possible (light source should be substantially a point source). Hence, when such projection type display apparatus uses a large number of LEDs, it becomes important to optically focus lights from the respective LEDs with high efficiency.
Official gazette of Japanese laid-open patent application 2000-112031 discloses a light source apparatus in which light from an LED array 102 with a plurality of LEDs 101 arrayed thereon in a two-dimensional fashion is reflected on a hollow optical guide block 103 with the same sectional area as that of the LED array 102 and in which reflected light is emitted from the cross-section of this optical guide block 103 as shown in FIG. 2.
However, according to this light source apparatus, since the light emission area (cross-section of the optical guide block 103) is the same as the area of the LED array 102, if the number of LEDs 101 is increased to increase luminance, then the light emission area is widened considerably. Accordingly, it is not possible to optically focus lights from a large number of LEDs with high efficiency.
In view of the aforesaid aspect, it is an object of the present invention to realize a light source with high luminance and high focusing efficiency suitable for use with a projection type display apparatus or the like by using LEDs.